The invention relates generally to the field of data links between central processing units and peripherals, and specifically, to serial transfer of parallel data by time division multiplexing through light conducting fibers. In the past, links for transfer between a CPU and peripherals have been either in serial or parallel format. However, most of these links have utilized copper conductor cables. Parallel links were favored because of increased speed even though such links were more expensive to design and build.
The speeds and lengths at which these parallel copper links could function were limited by the physical characteristics of the cable and the physics of electrical data transmission. For example, the geometry and composition of the cables resulted in losses due to impedance of the cables. In addition, the inherent stray capacitance in these cables slowed rise times thereby hindering speed. Minimizing these characteristics by altering the physical structure of the electrical cable is expensive.
On the other hand, the physics and material properties of optical fibers result in lower losses during transmission. Further, these losses are uniform up to a few hundred megahertz resulting in a large bandwidth. This broad bandwidth enables extremely high data transfer rates with little loss in performance. For example, an optical cable TV installation designed by the Harris Corporation in London Ontario will be operating at 322 megabits per second in mid-1979 at repeater spacings of 2.6 kilometers. Harris has also designed a 51 kilometer 274 megabit optical phone link scheduled for completion in late 1979. The useful lives of these optical links are expected to be from twenty to thirty years as opposed to five to seven years for an electrical link.
Further, the performance of fiber optic devices is being continually improved, and, as seen in the integrated circuits industry in the 1970's, prices for optical components will continue to fall as mass production techniques are devised and perfected.
In the computer industry, there are many applications suited for fiber optices. The large number of wires that connect CPU's to peripherals can be drastically reduced in size and number. In addition, longer links are feasible making possible distributed processing systems with CPU's spaced several kilometers apart as opposed to several feet apart. Thus the distance a peripheral may be spaced from its CPU no longer needs to be a limiting parameter of a computer system. Also noisy mechanical peripherals such as card readers, punches and printers may be placed in a different room from that of the CPU. Extra electrical noise immunity also results from use of optical fibers since radio frequency interference and cross talk via inductive coupling cannot occur.
Other remaining advantages of optical links include: ground loop elimination, size and weight reduction, no spark or fire hazard, higher transmission security, no short circuit loading, no ringing or echoes, and the ability to operate at temperatures up to 1000.degree. C.